Communications systems, and specifically messaging and paging systems, are arranged to reliably deliver information as long as the selective messaging unit (SMU) is within coverage range of the infrastructure. However, it may be economically impractical to deploy messaging and paging systems, either initially or during expansion, that completely guarantee coverage for a SMU anywhere within the system. Anytime that coverage is lacking or marginal a user or SMU may miss or fail to receive a message. Often the user will not realize they have missed a message. Some messaging and paging units, two way and one way units, will notify, using a visual status indication, the user of range or coverage status, thus providing some notice of potential missed messages. However this still requires the user to monitor the status indication and this may be overly burdensome particularly in unfamiliar areas. The potential or actual loss of messages is clearly a problem or significant inconvenience for subscribers that need messaging or paging coverage.
Those inconveniences or concerns spawned the concept of a message sequence number corresponding to each message for a given subscriber or SMU. The message sequence number allowed the selective messaging unit to track the messages received from the selective messaging system and to display this information for the subscriber. A message sequence number (MSN) is selected by the infrastructure or selective messaging system from a predetermined, usually sequential, numbering scheme. Subscribers by observation note the message sequence numbers successfully received, thus those that are not received and contact the service provider for a re-transmission of those that have not been successfully received.
Issues arise when the selective messaging unit is still out of range when re-transmission is requested as the system inefficiently uses airtime by attempting to re-send messages and of course the message is still not received. Additionally any utility depends on the subscriber noting irregularities in the sequence of message sequence numbers.
Two way selective messaging units have the ability to communicate with the infrastructure and can be arranged to recognize is certain irregularities in the message sequence number. Thus many of the problems that result from reliance on subscriber observation can be effectively dealt with by two-way units. However, message reconciliation problems that arise due to continuing lack of coverage, such as often found inside buildings, are not presently satisfactorily handled by either one-way or two way selective messaging units and systems.
Clearly a need exists for more effective missing message reconciliation.